A leading solicitor has expressed concern that London courts are "creaking" and may not be able to cope with the additional pressures that arise during the Olympics - when some courts will be holding fewer sittings.

Julian Young said the criminal justice system needed to be ready for a rise in crime during the games, with an influx of foreign visitors and the potential for fights to break out between rival groups of supporters.

The Guardian has learned that contingency plans are in place in case there are higher levels of crime during the Olympics. It's thought these could include courts sitting late into the evening.

Young, a solicitor-advocate who practises from modern (though far from spacious) offices near Westminster magistrates' court in Marylebone, told me that two of his clients had been unlawfully detained because of recent failings by the courts.

One defendant appeared for sentence at Thames magistrates court last Thursday on a video link from prison. The court passed a suspended sentence, meaning that he was entitled to be released immediately.

However, the prison refused to release Young's client until it had seen a copy of the court order. Young says that he and his assistant spent six or seven hours on the phone between them, trying to get court staff to fax the order to the prison.

Following my own call to HM courts and tribunals service, Young's client was released late on Friday.

"I'm livid," the solicitor told me. "It should not take 24 hours for someone to be released." He thought his client would be seeking compensation for unlawful imprisonment and said the case demonstrated the drawbacks of so-called virtual courts.

Young's second complaint is all the more extraordinary in the light of an unrelated case arising from the RBS computer failure last week. It emerged that a defendant who was granted bail at Canterbury crown court had to spend a weekend in custody because he was unable to show that bail money had been paid into court.

Young's client, who was facing fraud charges, had been granted bail on a Saturday in May on condition that he lodged "security" of £450 against the risk he might abscond. The defendant produced the money in cash, but the court refused to accept it on the ground that he did not have a bank account to which it could be returned once he surrendered to his bail.

Young explained that his client was a foreign national who did not have a UK bank account. But the court refused to accept the proffered cash and the defendant had to remain in custody on the Saturday and Sunday night.

The next day, Young made a fresh application to the magistrates, who ordered court staff to take the defendant's cash and release him from custody.

It is understood that the courts and tribunals service have accepted that the officials who refused to accept the cash over the weekend were guilty of maladministration. Young's client has been offered an apology and compensation of more than £700.

The courts service has also offered to pay the solicitor's costs, since his successful application for bail was not covered by legal aid.

Young is concerned that failures such as these may be multiplied during the Olympic games, as foreign visitors are unlikely to have UK bank accounts. He is also concerned that defendants will have to spend more time in custody awaiting trial because their trials are being postponed.

"These are real problems that must be addressed before the Olympics start," he said.

The courts and tribunal service confirmed that some cases due to be heard during the games would be postponed, although others would be heard sooner.

"Most of the courts and tribunals in London will be operating normally during the Olympics, and will deal with all urgent applications and cases," a spokesman said. "We have only reduced court and tribunal sittings at those buildings close to Olympic venues and known travel hotspots and are in the process of rescheduling listings to ensure that any displaced work is dealt with either before or in the weeks immediately after the games."

Officials are concerned that jurors and witnesses will have difficulty in getting to court because of pressure on public transport during the games. There must also be concerns that some jurors will be tempted to stay at home and watch crucial games on television.

The courts and tribunals spokesman disclosed that plans were in place to deal with unexpected crime surges.

"The HMCTS Olympics planning group has developed, with partner agencies, contingency plans in the event that there is a higher level of crime than expected," he said.

No details were given of what these might be, but everyone must hope they prove to be sufficiently robust.